When SIGSTOP is sent to a process, the usual behaviour is to pause that process in its current state. The process will only resume execution if it is sent the SIGCONT signal. SIGSTOP and SIGCONT are used for job control in the Unix shell, among other purposes. SIGSTOP cannot be caught or ignored.

When SIGSTOP or SIGTSTP is sent to a process, the usual behaviour is to pause that process in its current state. The process will only resume execution if it is sent the SIGCONT signal. SIGSTOP and SIGCONT are used for job control in the Unix shell, among other purposes.

In short, SIGSTOP tells a process PID to “hold on” and SIGCONT tells a process to “pick up where you left off”.

This work very well if one process needs a lot of memory and you need this memory now – you can pause a process and continue it.